By the way,

does anyone know how to lock up X in a really secure way? I have to
leave my office many time a day and i use xlock to lock my wm but one
can do crtl+alt+backspace to kill the x server or use crtl+alt+f[1-4] to
change to console. 

Is it possible to disable these functions and without using a kdm or
cdm? 

Tobias